1. Field of the Invention
The present invention relates to optical monitoring and more particularly concerns optical monitoring methods and apparatus and an improved point light source therefor.
2. Description of Related Art
The present invention is applicable to measurement, analysis and inspection of various types of apparatus and can be used for optical monitoring in many different situations. The invention has been specifically designed and initially used for measurement of so-called "orange peel" effect of a painted surface. This effect is caused by small, closely spaced wrinkles of the paint surface. It is a measure of how smooth the top surface of the paint appears. Orange peel effect is presently measured subjectively, by eye. Prior meters, although capable of measurement of some parameters of paint quality, are unable to directly measure orange peel as an independent parameter. In the past a laser and position sensor have been used Helium neon lasers employed for such purposes are large and expensive. Where a solid state laser is substituted, the cost, power supply drain and power supply size are still serious handicaps. Other methods of optical inspection include detection of the edge of a projected image. The use of an image in this fashion requires relatively complex focused optics Such optics mean that focal length and focal positions are very critical, requiring careful control of distances to and from the paint surface. These problems and the significantly large size of such devices cause such inspection devices to be user sensitive and difficult to operate in a manner that will provide reliable, repeatable data.
Applicant is unaware of prior devices that directly measure orange peel. However, measurement of orange peel is important in the painting of automobiles because this effect is a major cause of poor paint jobs. Orange peel at present is quantified by subjective judgment, that is, by an individual, personal observation of the surface Orange peel is caused by various parameters of the paint process itself including humidity, temperature, and amount of solvent in the paint. If there were available an objective quantitative measure of orange peel it would be possible to relate such measure to process parameters so that the process could be corrected to decrease the adverse orange peel effect.
In some situations, such as the painting of large electrical appliances or computer housings, for example, it is desirable to obtain some degree of orange peel on the final paint surface. Nevertheless there still is lacking any way to quantify the amount of intended surface roughness for quality control.
Paint inspection meters of the prior art have measured other parameters of paint quality, such as gloss, color purity, and distinctness of image. The latter is defined as the distinctness of an image reflected from a painted surface. However, none of these prior devices can directly measure orange peel as an independent parameter. Further, prior paint inspection meters are neither small nor easy to handle. Prior art devices require two hands and, although they may be portable, are not readily transported and used by a single hand. Prior meters are often subjective in use so that different operators will obtain different results. Such measuring devices also require longer periods of time to make a measurement or may require cable attachment to power supplies and other stationary circuitry.
In my co-pending application for Hand Held Inspection Meter, identified above, a simple hand held paint inspection meter is described employing as a light source either a conventional light emitting diode and lens or a laser diode. However, the light emitting diode is not an effective point source, whereas the laser diode is expensive, requires significant amounts of power and is of a larger size.
Accordingly, it is an object of the present invention to provide optical monitoring methods and apparatus that avoid or minimize above mentioned problems.